This is quite straightforward:

1. Determine exactly what type phone you have now, as per WDS
2. Remove old telephone control unit
3. Adapt wiring of telephone connector (if necessary) to suit TCU
4. Connect TCU and code as required.

You are not the first to do this...

NOTE: you will currently have a separate SES module for voice recognition (VR), you can choose to retain this or replace the VR with the TCU VR (TCU = phone VR only)